In a known piezoelectrically actuated fuel injector, a piezoelectric actuator is operable to control the position occupied by a control piston, the piston being moveable to control the fuel pressure within a control chamber defined, in part, by a surface associated with the valve needle of the injector to control movement of the injector. Such an arrangement suffers from the disadvantage that fuel tends to leak from the control chamber past the piston, such a parasitic escape of fuel resulting in the injector being relatively inefficient. Further, during injection, the restriction to fuel flow formed by the passages and fuel lines whereby the injector is connected to a common rail may result in the fuel injection pressure falling to an unacceptable level.
Another problem with known injectors is that pressure waves transmitted along the fuel passages and lines may give rise to undesirable needle movement during injection and may be of sufficient magnitude to cause secondary injections.